Opossums

Opossum Facts

Classification:

• Kingdom: Animalia
• Subkingdom: Bilateria
• Phylum: Chordata
• Subphylum: Vertebrata
• Class: Mammalia
• Subclass: Theria
• Order: Didelphimorphia
• Family: Didelphidae
• Genera:Caluromys (bare-tailed woolly opossums, four species);Didelphis (large American opossums, six species);Gracilinanus (gracile opossums, nine species);Marmosa (mouse opossums, nine species);Marmosops (slender opossums, fourteen species);Micoureus (woolly mouse opossums, six species);Monodelphus (short-tailed opossums, eighteen species); Philander (black or gray four-eyed opossums, four species); Thylamys (fat-tailed opossums, ten species); eight other genera, with one species each
• Geographical location: North, Central, and South America; Caribbean
• Habitat: Forests, grasslands, mountains, and swamps
• Gestational period: Twelve to fourteen days
• Life span: From one to three years in the wild, up to ten years in captivity
• Special anatomy: Opposable thumblike toe on the hind foot, prehensile tail, pouch

Opossums represent the oldest surviving mammal family. Ancestors resembling modern opossums lived on earth at the same time as the dinosaurs. Scientists have located seventy-million-year-old opossum fossils. The Virginia opossums are found in the United States and Canada, while other relatives of the Didelphidae family live in Central and South America as well as the Caribbean islands. They are believed to have originated in South America and gradually moved northward after the continents of North and South America joined.

Anatomy

The Virginia opossum is the largest species of the Didelphidae family. They are about the size of a domestic cat and measure from 0.3 to 0.8 meters (1 to 2 feet) in length, with a 22 to 50 centimeter (9 to 20 inch) long tail. Their weight varies from 2 to 5.5 kilograms (4 to 12 pounds). Other opossums are much smaller, averaging 7.5 centimeters (3 inches) in length with a 5 to 10 centimeter (2 to 4 inch) long tail.

Opossums have varying lengths and thicknesses of fur, in shades of white, gray, brown, and black. Some opossums have stripes. Opossum eyes are black or brown, and their ears are usually hairless. Their faces have a mask or are white. They have a pink nose at the end of a long, pointed, whiskered snout, which has fifty sharp teeth. Their four feet and tail are also pink and hairless. Each forefoot has five toes with claws. Opossums have an opposable, thumblike toe on their hind feet that can grasp objects and cling to branches. They are arboreal animals and agile climbers. Their prehensile tails are used for balance.

Life Cycle

Male opossums attain maturity at eight months, and females are sexually mature between six and nine months. Female opossums can produce two litters annually. As many as fifty-six offspring may be in a litter, but because female opossums can only nurse thirteen newborns in their marsupium, many newborn opossums may die. The average litter size is seven to eight, however.

Born blind, each newborn opossum, which is almost embryonic and as small as a bean, crawls from the birth canal near their mother’s tail and across her stomach to her pouch. They attach to nipples inside the pouch, where they nurse for two to three months. This nursing period provides them with immunities to diseases. The babies stay inside the pouch when the mother leaves the den to forage. As they grow and the pouch becomes full, the young opossums sometimes briefly leave the pouch, then return for nourishment. From the age of three to five months, the babies ride on their mother’s back. While traveling this way, the young opossums gain scavenging and survival skills.

Behavior

Opossums tend to be solitary, nomadic animals that can range over 30 to 96 acres (0.5 to 1.5 square miles) daily. They nest in hollow trees and other animals’ burrows. Opossums are nocturnal, foraging at night. Because they are adaptable, opossums can live in a variety of habitats and are frequently found in urban areas which formerly were wooded. They adjust their scavenging and living habits to find food and shelter whether they are in a rural setting or in the middle of a city. Extremely cold weather is the primary environmental condition that deters opossums from otherwise suitable habitats. Opossums are hardy and immune to most diseases. They are the mammal most resistant to rabies.

Opossums are omnivorous and eat a variety of insects, especially crickets, beetles, and cockroaches. They also consume snails, slugs, deer ticks, snakes, worms, birds, and rodents in addition to carrion and eggs. Berries, fruit, and vegetables appeal to opossums, particularly when overripe. Opossums have keen senses of smell, vision, and hearing to locate sustenance and clean up organic wastes in their territories.

The life expectancy of opossums is one to three years in the wild and as many as ten years when kept in captivity. They are immune to bee and scorpion stings, botulism, and snake venom, and resistant to rabies and Lyme disease. In addition to being preyed upon by wildlife such as wild dogs, bobcats, and birds of prey, as well as domesticated animals, opossums are killed by humans for sport, fur, meat, or medicinal use, or by accident with vehicles. Baby opossums often survive automobile impacts that kill their mothers.

Opossums show a variety of defense mechanisms: they move more slowly than their predators and often spray a foul-smelling secretion to thwart attacks. Virginia opossums feign death by becoming limp when frightened and unable to escape. They sometimes hiss or growl, exposing their teeth. Opossums occasionally fight and bite. Opossums hide in brush-covered areas that are difficult for predators to access. They can make sounds, including screeches, but are usually quiet. Scientists have gauged opossums’ ability to learn and distinguish objects as greater than that of dogs and almost equivalent to pigs. Their problem-solving skills surpass those of rats and cats.

The National Opossum Society offers information about how people can rehabilitate injured opossums and raise orphans. The group also addresses the controversial use of opossums as laboratory research specimens.

Principal Terms

arboreal: living in trees

carrion: rotting carcasses

marsupium: pouch

opposable: positioned opposite of other objects

prehensile: wrapping

Bibliography

Allen, Thomas B., ed. Wild Animals of North America. National Geographic Society, 1995.

Gardner, Alfred L., and Melvin E. Sunquist. “Opossum (Didelphis virginiana).” Wild Mammals of North America: Biology, Management, and Economics, edited by George A. Feldhammer and Bruce Thompson, Johns Hopkins UP, 2003, pp. 3–29.

Krause, W. J. A Review of Histogenesis/Organogenesis in the Developing North American Opossum (Didelphis virginiana). 2 vols. Heidelberg: Springer-Verlag, 1998.

Lipske, Michael. "Give Opossums a Break: Why It Makes Sense to Make Way for Opossums in Your Garden." National Wildlife, 30 Mar. 2015. National Wildlife Federation, 1999–2016, www.nwf.org/News-and-Magazines/National-Wildlife/Animals/Archives/2015/Opossums.aspx. Accessed 6 Oct. 2016.

Martina, Leila Siciliano. "Didelphis virginiana, Virginia Opossum." Animal Diversity Web (ADW), 2013. University of Michigan Museum of Zoology, 2014, animaldiversity.org/accounts/Didelphis‗virginiana. Accessed 6 Oct. 2016.

Seidensticker, John, with Susan Lumpkin. “Playing Possum Is Serious Business for Our Only Marsupial.” Smithsonian vol. 20, no. 8, 1989, pp. 108–19.